Nickel(II) and palladium(II) complexes with an alkane-bridged macrocyclic ligand: Synthesis, characterization, and polymerization tests

Article abstract of DOI:10.1021/om0503904

An efficient synthetic route to a novel macrocyclic aryl α-diimine ligand bearing C₆ hydrocarbon bridges connecting the aryl ortho positions is described. Pd(II) and Ni(II) complexes with the new macrocyclic ligand (10 and 14) were successfully synthesized and characterized. The X-ray crystal structures of complexes 10 and 14 show that the complexes exhibit coordination geometry similar to that of their acyclic analogues and the alkyl bridges do not introduce significant ring strain into the complexes. The preactivated Pd(II) complex 12 and the allyl nickel complex 14 were tested for ethylene polymerization. Potential reasons for the low catalytic activities are discussed.

Full text of DOI:10.1021/om0503904

Organometallics 2005, 24, 4933-4939
4933
Nickel(II) and Palladium(II) Complexes with an
Alkane-Bridged Macrocyclic Ligand: Synthesis,
Characterization, and Polymerization Tests
Drexel H. Camacho, Eric V. Salo, Zhibin Guan,* and Joseph W. Ziller
Department of Chemistry, 516 Rowland Hall, University of California,
Irvine, California 92697-2025
Received May 14, 2005
An efficient synthetic route to a novel macrocyclic aryl R-diimine ligand bearing C6
hydrocarbon bridges connecting the aryl ortho positions is described. Pd(II) and Ni(II)
complexes with the new macrocyclic ligand (10 and 14) were successfully synthesized and
characterized. The X-ray crystal structures of complexes 10 and 14 show that the complexes
exhibit coordination geometry similar to that of their acyclic analogues and the alkyl bridges
do not introduce significant ring strain into the complexes. The preactivated Pd(II) complex
12 and the allyl nickel complex 14 were tested for ethylene polymerization. Potential reasons
for the low catalytic activities are discussed.
Chart 1
Introduction
In polymerization catalyst design both ligand elec-
tronics and sterics play important roles in determining
the catalyst activity and polymer molecular weight. One
remarkable example of ligand steric effects can be found
in the development of late transition metal polymeri-
zation catalysts. For the Shell higher olefin process
(SHOP) catalyst, in which Ni(II) is complexed to a ligand
without steric bulk, â-H elimination and chain transfer
compete favorably with chain growth and short R-olefins
are formed as the major products. The fast chain
transfer in late transition metal catalysts is generally
believed to be through an associative process, in which
olefin monomer associates from the axial direction of
the metal center and replaces a terminal polymer olefin
formed from â-H elimination. To suppress the facial
chain transfer, Brookhart and co-workers developed Ni-
(II) and Pd(II) complexes with bulky R-diimine ligands
that are highly productive for olefin polymerization and
form high molar mass polyolefins (1 in Chart 1).1-3
Although â-H elimination is still competitive with chain
propagation in Brookhart catalysts, as manifested by
chain walking to form branched polymers,1-8 the steri-
cally encumbered R-diimine ligands prevent associative
exchange following the formation of olefin-hydride spe-
cies.9 A systematic correlation was observed between
polymer molecular weight and the ortho-aryl subsituent
size in R-diimine ligands, with the more bulky substitu-
ent affording higher polymer molecular weight.10 In
other late transition metal polymerization catalysts,
ligand sterics are also found to have significant effects
on polymer molecular weight.11
To completely shut down associative chain transfer
from the axial direction for the R-diimine-Ni(II) and -Pd-
(II) catalysts, our group recently developed a cyclo-
phane-based R-diimine ligand for Ni(II) and Pd(II)
complexes for the preparation of highly productive and
robust olefin polymerization catalysts (2 in Chart 1).12-15
In our cyclophane-based complexes, the metal center is
positioned at the core of the ligand so that the macro-
cycle completely blocks the axial faces of the metal,
leaving only two cis-coordination sites for monomer
entry and polymer growth. The rigid framework of the
ligand prohibits free rotation of the aryl-nitrogen
bonds, which should allow the catalyst to make high
MW polymers at elevated temperature. The lack of
rotational flexibility should also prevent C-H activation
to the ortho subsitutents, which was proposed to be a
* To whom correspondence should be addressed. E-mail: zguan@
uci.edu.
(1) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414-6415.
(2) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.
1996, 118, 267-268.
(3) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.
Chem. Soc. 1998, 120, 888-899.
(10) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320-
2334.
(4) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J. Science 1999,
283, 2059-2062.
(11) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460-462.
(12) Guan, Z.; Camacho, D. H. In PCT Int. Appl. WO 2005014658,
2005, 43 pp.
(5) Guan, Z. Chem. Eur. J. 2002, 8, 3086-3092.
(6) Guan, Z. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 3680-
3692.
(7) Chen, G.; Ma, X. S.; Guan, Z. J. Am. Chem. Soc. 2003, 125, 6697-
6704.
(8) Chen, G.; Guan, Z. J. Am. Chem. Soc. 2004, 126, 2662-2663.
(9) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart,
M. J. Am. Chem. Soc. 2000, 122, 6686-6700.
(13) Camacho, D. H.; Salo, E. V.; Ziller, J. W.; Guan, Z. Angew.
Chem., Int. Ed. 2004, 43, 1821-1825.
(14) Camacho, D. H.; Salo, E. V.; Guan, Z. Org. Lett. 2004, 6, 865-
868.
(15) Camacho, D. H.; Guan, Z. Macromolecules 2005, 38, 2544-2546.
10.1021/om0503904 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/08/2005

4934 Organometallics, Vol. 24, No. 21, 2005
Camacho et al.
Scheme 1
Scheme 2
potential catalyst deactivation pathway by Brookhart
and co-workers.9 Indeed, we were pleased to observe
that our cyclophane-based Ni(II) and Pd(II) catalysts
have significantly higher thermal stability than the
acyclic analogues.13 The Ni(II)-cyclophane catalyst was
extremely productive for ethylene polymerization to
form high molecular weight polyethylene at a range of
temperatures.13 The Ni(II) complex was also able to
initiate living polymerization of R-olefins at elevated
temperatures.15 We recently discovered that our cyclo-
phane-based Pd(II) catalyst is much more efficient in
incorporating polar olefins such as methyl acrylate.16
In our further efforts on investigating macrocyclic
ligands for olefin polymerization catalysis, we recently
synthesized an alkane-bridged macrocyclic R-diimine
ligand 3 (Chart 1). Following a similar concept for our
m-terphenyl-based cyclophane ligand 2, ligand 3 is
designed to have the two aryl groups being connected
by alkyl bridges with the R-diimine moiety situated in
the core of the macrocycle. By using alkyl bridges, ligand
3 is viewed as a structurally closer macrocyclic analogue
of ligand 1. The hydrocarbon bridge is envisioned to
shield the axial positions of the metal center, which
should play an important role in suppressing the
associative chain transfer in olefin polymerizations.17
On the basis of these considerations, we have synthe-
sized the ligand 3 and its corresponding Ni(II) and Pd-
(II) complexes. Herein we report the synthesis, charac-
terizations, and ethylene polymerization attempts of
these complexes.
starting material instead of its aniline analogue was to
avoid complication with the subsequent Grignard reac-
tion. With the treatment of allylmagnesium chloride, 5
underwent clean substitution at the benzylic positions
to give 6 in 90% yield. The bromine at the benzene ring
was not affected even with excess allylmagnesium
chloride. The next step was a critical transformation in
which bromobenzene 6 was converted to aniline 7. The
key to effect this transformation was the choice of
trimethylsilylmethyl azide as the aminating agent.19
Thus, treatment of 6 with Mg gave the corresponding
Grignard reagent, which upon addition of trimethylsi-
lylmethyl azide and subsequent aqueous workup af-
forded aniline 7 in 72% yield.19,20 The resulting aniline
was conveniently converted to R-diimine 8 by condensa-
tion with acenaphthenequinone. Initial attempts of
cyclization of 8 by ring closing metathesis (RCM) of 8
in dichloromethane using generation 1 or 2 of the
Grubbs ruthenium carbene catalysts only afforded a
monocyclic product. Computer modeling shows that once
the first ring is formed, the opposite side of the aryl
opens up, thus making it harder for the remaining
olefins to come in proximity, which presumably in-
creases the activation barrier for the second ring-closing
reaction. On the basis of this consideration, more
forceful conditions were investigated to achieve the
double cyclization by RCM. After optimizing reaction
conditions, RCM in toluene at 90 °C21 in combination
with slow addition of the Grubbs catalyst with time gave
product 9 in 70% yield,22 which was further hydroge-
nated to provide the final product, 3, in 92% yield. The
1
structure of 3 was characterized by H and 13C NMR
Results and Discussion
and combustion analysis.
A. Synthesis and Characterization of Alkane-
Bridged r-Diimine Ligand. The key step of macro-
cycle formation in the synthesis of 3 was achieved by
ring-closing metathesis (RCM) of an R-diimine precursor
containing terminal olefins. This required the prepara-
tion of aniline 7, containing two terminal alkene sub-
stituents at ortho positions of the phenyl ring. On the
basis of molecular modeling, a six-methylene bridge
(-(CH2)6-) seems to have an ideal fit to the spacing
between the two phenyl rings in the R-diimine. There-
fore, four-carbon 1-butenyl substituents were first in-
stalled onto the ortho positions of aniline 7. The
synthesis started with the R-bromination of the com-
mercially available 2-bromometaxylene 4 to give 5 in
good yield.18 The choice of the bromobenzene 4 as
B. Synthesis and Structural Characterization of
Ni(II) and Pd(II) Complexes with the Alkane-
Bridged r-Diimine Ligand. Synthesis and Char-
acterization of Pd(II) Complexes. With ligand 3 in
(16) Popeney, C.; Camacho, D.; Guan, Z. Unpublished results.
(17) A hemicyclic ligand has been described in a Ph.D. Thesis:
Small, B. L., Ph.D. Thesis, University of North Carolina Chapel Hill,
1998; Chapter 2, pp 15-23.
(18) Bibal, C.; Mazie`res, S.; Gornitzka, H.; Couret, C. Polyhedron
2002, 21, 2827.
(19) Nishiyama, K.; Tanaka, N. Chem. Commun. 1983, 1322.
(20) Tsuge, O.; Kanemasa, S.; Matsuda, K. Chem. Lett. 1983, 1131.
(21) Efskind, J.; Undheim, K. Tetrahedron Lett. 2003, 44, 2837.
(22) The TLC of the reaction shows three close spots with the same
molecular mass, suggestive of cis/trans product ratios. The fractions
are combined and used for the hydrogenation step.

Ni(II) and Pd(II) Complexes with Macrocyclic Ligand
Organometallics, Vol. 24, No. 21, 2005 4935
Scheme 3
Scheme 4
was synthesized by following a methodology recently
developed in our laboratory.24 Due to steric encum-
brance of the macrocyclic ligand, direction methylation
of the PdCl2 complex 10 with various methylation
reagents (such as Sn(CH3)4) was not successful. In our
previous studies, we have developed an efficient strategy
of synthesizing sterically encumbered LPd(Me)Cl com-
plexes by in situ generation of (PhCN)2Pd(Me)Cl fol-
lowed by exchange of the labile benzonitrile (PhCN)
ligand with the desired chelating ligand.24 As shown in
Scheme 5, this strategy was successful for the synthesis
of the Pd(Me)Cl complex 11 in 80% yield. The complex
11 was subsequently activated by sodium tetrakis[3,5-
bis(trifluoromethyl)phenyl] borate (NaBAF) followed by
addition of methyl acrylate to give the preactivated Pd-
(II) catalyst 12 in 95% yield as a brick red solid.
Synthesis and Characterization of Ni(II)-Allyl
Complex. Our initial attempts for the preparation of
NiX2 complexes with ligand 3 using (DME)NiBr2, (DME)-
NiCl2, and NiF2, respectively, as precursors were not
successful. Presumably, the tetrahedral geometry of Ni-
(II) halide complexes prevents them from coordinating
to the macrocyclic ligand due to the sterics imposed by
the bridges on both sides of the imine plane. Attempts
to make the planar dimethyl complex were also unsuc-
cessful. After many attempts, finally we succeeded in
preparing the nickel-allyl complex of ligand 3. Treating
the ligand with π-allyl nickel chloride dimer25 and
sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
(BAF) afforded the corresponding η3-allyl(R-diimine)-
nickel complex 14 in 67% yield (Scheme 6).
hand, various Ni(II) and Pd(II) complexes with it were
prepared. First, a PdCl2 complex with the new ligand
(3) was prepared by mixing PdCl2(CH3CN) with ligand
3 in dichloromethane. The complexation was evident by
1
a change in color from orange to red-orange. H NMR
monitoring of the complexation indicated that the
reaction was complete within 6 h to give complex 10.
High-quality single crystals suitable for X-ray analysis
for the Pd(II) complex 10 were obtained by carefully
layering a slightly concentrated dichloromethane solu-
tion of 10 with n-decane. The X-ray crystal structure of
complex 1023 (Figure 1) shows a square planar coordi-
nation geometry with the Pd(II) center being positioned
in the core of the cyclophane ligand. The alkyl bridges
lie above and below the coordination plane. The torsion
angles between the five-membered palladacyclic coor-
dination plane (Pd1-N1-C1-C11-N2) and the two
aryl planes (C13-C18 and C25-C30) are 76.7° and
77.4°, respectively. These are very close to the values
for an acyclic Pd(II)-R-diimine complex (78.6° and 79.4°)
reported by Brookhart and co-workers,9 indicating that
the alkane bridges do not introduce significant ring
strain to the complex. The crystal data and structure
refinement parameters and selected bond lengths, angles,
and interplanar angles of complex 10 are summarized
in Tables 1 and 2, respectively.
Complex 14 was fully characterized by NMR, high-
resolution mass spectroscopy (HRMS), and X-ray crystal
analysis. The X-ray crystal structure of complex 1426
(Figure 2) shows that the Ni(II) complex has a coordina-
tion geometry similar to that of complex 10. The Ni(II)
center is coordinated to the bidentate R-diimine and the
π-allyl ligand in a square planar coordination geometry.
Because PdCl2 complexes usually are not good pre-
cursors for direct activation by methylaluminoxane
(MAO) for olefin polymerization, a preactivated Pd(II)
complex was then synthesized for the polymerization
test. In the first step, a Pd(Me)Cl complex of ligand 3
Figure 1. X-ray crystal structure of the PdCl2 complex 10 showing important atoms labeled: (a) front view and (b) side
view (n-decane solvent molecule was removed for clarity; the atoms were drawn with 50% thermal ellipsoids).

4936 Organometallics, Vol. 24, No. 21, 2005
Camacho et al.
Table 1. Summary of Crystal Data and Structure
Refinement Parameters of Complexes 10 and 14
the other slightly below it (see Supporting Information).
The torsion angles between the five-membered coordi-
nation plane (Ni1-N1-C4-C14-N2) and the two aryl
planes (C16-C21 and C28-C33) are 76.7° and 80.0°,
respectively. Again, these values are very close to the
corresponding torsion angles for the Pd(II) complex 10
and the Brookhart acyclic Pd(II)-R-diimine complex,9
suggesting that the alkyl bridges do not introduce
significant ring strain to the complex. The crystal data
and structure refinement parameters and selected bond
lengths, angles, and interplanar angles of complex 14
are summarized in Tables 1 and 2, respectively.
C. Ethylene Polymerization Tests and Discus-
sion. Following the synthesis and structural charac-
terization, both the preactivated Pd(II) complex 12 and
Ni(II)-allyl complex 14 were tested for ethylene polym-
erization. To our disappointment, under a variety of
ethylene pressures and polymerization temperatures
the Pd(II) complex 12 afforded only a trace amount of
polyethylene (TON < 10). The Ni(II)-allyl complex 14,
upon activation with tris(pentafluorophenyl)borane,
again yielded only a trace amount of polymers. For the
Ni(II) complex, we also attempted in situ generation of
the 3-NiBr2 complex, which upon activation by MMAO
also gave low activity for ethylene polymerization (TON
< 400). The unanticipated low polymerization activity
for the Ni(II) and Pd(II) complexes prompted us to
reexamine their structures more carefully.
10
14
empirical formula
fw
C
36H36Cl2N2Pd‚1/2C10H22 C71H53BF24N2Ni
745.11
1459.67
red
cryst color
cryst syst
space group
a (Å)
orange
monoclinic
P21/c
monoclinic
P21/n
12.7132(11)
11.5066(10)
24.026(2)
90
93.064(2)
90
21.472(2) Å
14.6907(15) Å
21.881(2) Å
90
111.013(2)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
3509.6(5)
4
6443.0(11)
4
Z
density (Mg/m3)
1.410
1.505
abs coeff (mm-1
F(000)
)
0.713
1548
0.416
2968
cryst size (mm)
scan mode
detector
θ range for data
collection (deg)
index ranges
0.34 × 0.32 × 0.22
0.35 × 0.26 × 0.20
ω
ω
Bruker-CCD
1.60 to 28.30
Bruker-CCD
1.14 to 24.71
-16 e h e 16,
-15 e k e 15,
-32 e l e 31
35 898
-20 e h e 25,
-16 e k e 17
-25 e l e 25
32 601
no. of reflns
collected
no. of indep reflns 8470 [R(int) )
10 856 [R(int) )
0.0259]
98.8%
0.0205]
97.2%
completeness to
θ ) 28.30°
abs corr
semiempirical from equivalents
max. and min.
transmn
0.8589 and
0.7936
0.9214 and
0.8681
The space-filling representation of the X-ray crystal
structures for 10 and 14 are shown in Figure 3. To
better view the sterics imposed by the ligand environ-
ment to the metal sites, the chloride atoms in 10 and
the allyl fragment in 14 are truncated for clarity. It
appears that the catalytic sites in both complexes are
very crowded because of the alkyl bridges above and
below the coordination plane. Compared with the
Brookhart acyclic R-diimine complexes and our aromatic
cyclophane-based complexes, complexes 10 and 14 are
significantly more crowded at the metal centers. Be-
cause of the macrocyclic geometry, this high sterics
cannot be alleviated by conformational rotation. The
high sterics and rigid structure may either prevent the
entry of ethylene monomer or significantly increase the
insertion activation energy, resulting in reduction of
refinement method
no. of data/
restraints/
params
full-matrix least-squares on F2
8470/6/390
10 856/0/896
goodness-of-fit
1.067
1.037
on F2
final R indices
[I > 2σ(I)]
R1 ) 0.0482,
wR2 ) 0.1475
R1 ) 0.0628,
wR2 ) 0.1600
R1 ) 0.0772,
wR2 ) 0.1725
1.504 and -0.646
R indices (all data) R1 ) 0.0531,
wR2 ) 0.1520
largest diff peak & 3.034 and -0.946
hole (e‚Å-3
)
The alkyl bridges lie above and below the coordination
plane. The crystal data of 14 indicate that the allyl C1-
C3 unit is slightly disordered. The C2 can occupy two
positions: one slightly above the coordination plane and
Table 2. Selected Bond Lengths (Å), Angles (deg), and Interplanar Angles (deg) for 10 and 14
10 14
Bond Lengths
Ni(1)-N(2)
Pd(1)-N(2)
Pd(1)-N(1)
Pd(1)-Cl(2)
Pd(1)-Cl(1)
N(1)-C(1)
N(1)-C(13)
C(1)-C(2)
2.042(3)
2.045(3)
2.2800(8)
2.2815(8)
1.286(4)
1.438(4)
1.460(5)
1.486(5)
1.422(5)
1.936(3)
1.945(3)
2.021(4)
1.975(7)
2.016(4)
1.287(4)
1.434(5)
1.459(5)
1.481(5)
1.380(5)
Ni(1)-N(1)
Ni(1)-C(1)
Ni(1)-C(2)
Ni(1)-C(3)
N(1)-C(4)
N(1)-C(16)
C(4)-C(5)
C(4)-C(14)
C(5)-C(6)
C(1)-C(11)
C(2)-C(12)
Bond Angles
N(2)-Pd(1)-N(1)
N(2)-Pd(1)-Cl(2)
N(1)-Pd(1)-Cl(2)
N(2)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1)
Cl(2)-Pd(1)-Cl(1)
79.65(11)
95.12(8)
174.02(8)
174.58(8)
94.95(8)
90.30(3)
76.7
N(1)-Ni(1)-N(2)
N(1)-Ni(1)-C(1)
N(1)-Ni(1)-C(3)
N(2)-Ni(1)-C(1)
N(2)-Ni(1)-C(3)
C(1)-Ni(1)-C(3)
83.21(12)
101.44(16)
174.86(17)
174.26(16)
101.73(17)
73.5(2)
(C13-C18)-(Pd1-N1-C1-C11-N2)
(C25-C30)-(Pd1-N1-C1-C11-N2)
(C16-C21)-(Ni1-N1-C4-C14-N2)
(C28-C33)-(Ni1-N1-C4-C14-N2)
76.7
77.4
80.0

Ni(II) and Pd(II) Complexes with Macrocyclic Ligand
Organometallics, Vol. 24, No. 21, 2005 4937
Figure 2. X-ray crystal structure of the Ni(II)-allyl complex 14 showing important atoms labeled: (a) front view and (b)
side view (C2 is only shown for one position and the BAF counterion was removed for clarity; the atoms were drawn with
50% thermal ellipsoids).
Figure 3. Space-filling representation for the X-ray crystal structures of complexes 10 and 14: (a) PdCl2 complex 10; (b)
Ni(II)-allyl complex 14. (The two chloride atoms in 10 and the allyl fragment in 14 are removed for better visualization of
the sterics in the binding pocket. Color code: red ) Pd; purple ) Ni; gray ) C; white ) H; blue ) N.)
Scheme 5
Scheme 6
in complex 10 are 2.66 and 2.75 Å, while in Ni(II)
complex 14 the shortest distances are 2.56 and 2.57 Å.
The close proximity between alkyl hydrogens and the
metal centers may lead to C-H activation and further
catalyst deactivation via the pathway proposed by
Brookhart and co-workers.9 This may be an alternative
mechanism to account for their low catalytic activity.
The structural analysis suggests that, while ligand
bulkiness is important for achieving active catalyst and
high molecular weight polymer, a too crowded catalytic
center may prohibit catalytic activity. In future ligand
design, a balance of steric bulkiness in axial directions
and accessibility of the metal center from the front side
has to be reached in order to achieve highly active
polymerization catalysts.
polymerization activity. Figure 3 also shows that some
hydrogen atoms in the alkyl bridge are very close to the
metal centers in complexes 10 and 14. The shortest
distances between the Pd center and alkyl hydrogens
(23) The X-ray shows decane cocrystallizing as an impurity to give
an empirical formula of C36H36Cl2N2Pd‚1/2C10H22. CCDC 254673 con-
tains the supplementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax (+44) 1223-336-033; or
deposit@ccdc.cam.ac.uk).
Conclusions
(24) Salo, E.; Guan, Z. Organometallics 2003, 22, 5033.
(25) Wilke, G.; Bogdanovic, B.; Hardt, P.; Heimbach, P.; Keim, W.;
Kroner, M.; Oderkirch, W.; Tanaka, K.; Steinbrucke, E.; Walter, D.;
Zimmerman, H. Angew. Chem., Int. Ed. Engl. 1966, 5, 151.
(26) Careful layering of a DCM solution of 14 with decane and slow
evaporation of the solvents afforded high-quality single crystals. The
entire complex including the BAF counterion has an empirical formula
of C71H53BF24N2Ni. CCDC 254674 contains the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax (+44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
An efficient synthetic route was developed for the
preparation of novel alkyl-bridged cyclophane-type
ligands. With R-diimine as a template, ring-closing
metathesis afforded efficient cyclization to form two
alkyl bridges at one time. Using this methodology, the
new macrocyclic R-diimine ligand 3, containing two C6
alkyl bridges, was successfully synthesized. A series of
Pd(II) and Ni(II) complexes of 3 were successfully

4938 Organometallics, Vol. 24, No. 21, 2005
Camacho et al.
the magnesium, and the reaction is refluxed until all the
magnesium metals are gone. The reaction mixture was then
cooled to room temperature, and trimethylsilylmethyl azide
(1.55 g, 1.2 equiv) in ether was added dropwise. The reaction
was continued overnight at room temperature. Addition of
water and stirring for 30 min followed by the usual extraction
workup gave a crude mixture, which upon column chroma-
tography (silica, 10%ethyl acetate in hexane) gave the amine
products 7 in 72% yield.
prepared and characterized. The X-ray crystal struc-
tures of complexes 10 and 14 show that the complexes
exhibit coordination geometry similar to their acyclic
analogues and the alkyl bridges do not introduce
significant ring strain into the complexes. The preacti-
vated Pd(II) complex 12 and the allyl nickel complex
14 exhibited low activities for ethylene polymerization.
Careful structural analysis indicates that the alkyl
bridges impose significant sterics to the catalytic cen-
ters, which may cause a reduction of polymerization
activity. The proximity of some alkyl hydrogens to the
metal centers may also result in catalyst deactivation
via intramolecular C-H activation followed by decom-
position. This study points out that a number of molec-
ular parameters including the binding pocket size, the
geometry of the ligand, and a balance of steric bulkiness
in axial directions and accessibility of the metal center
from the front side have to be considered in future
polymerization catalyst designs.
7: 1H NMR(CDCl ) δ 6.96 (d, J ) 7.5 Hz, 2H); 6.72 (t, J ) 7.5
3
Hz, 1H); 5.97-5.89 (m, 2H); 5.14-5.02 (m, 4H); 3.64 (s, br,
2H); 2.64-2.60 (m, 4H); 2.43-2.38 (m, 4H); 13C NMR(CDCl )
3
141.8, 138.3, 127.3, 125.8, 118.2, 115.1, 34.3, 32.9, 31.2 ppm.
Anal. Calcd for C14H19N: C 83.53, H 9.51, N 6.96. Found: C
83.58, H 9.41, N 6.59.
Synthesis of 8. To a mixture of acenaphthenequinone and
aniline 7 (2.6 equiv) in methanol was added drops of formic
acid. The mixture was refluxed for 2 days, after which a yellow
solid precipitates out of the solution. Washing with cold
methanol and drying gave the diimine product as a yellow solid
in 82% yield.
8: 1H NMR(CDCl ) δ 7.90 (d, J ) 10.3 Hz, 2H); 7.38 (t, J )
3
9.6 Hz, 2H); 7.21-7.16 (m, 6H); 6.67 (d, J ) 8.9 Hz, 4H); 5.76-
5.69 (m, 4H); 4.82 (m, 8H); 2.66-2.49 (m, 8H); 2.34-2.21 (m,
8H); ESMS exptl (M + H) ) 549.32, obsvd (M + H) ) 549.25;
HRMS calcd for C40H40N2 [M + H]+ 549.3270, found 549.3278.
Anal. Calcd for C40H40N2: C 87.55, H 7.35, N 5.10. Found: C
87.57, H 7.35, N 5.13.
Synthesis of 9. A solution of 8 and Grubbs’ second-
generation catalyst in toluene was heated to 90 °C under
nitrogen atmosphere. The solution turns black after 1 h,
indicating the decompositon of the catalyst. Re-addition of the
catalyst in DCM was done every 2 h for four times. The
mixture was stirred at 90 °C overnight. Evaporation of the
solvent and column chromatography (silica, 4:6 DCM/hexane)
gave the cyclophane 9 in 70% yield.
Experimental Section
General Procedures. All manipulations of air- and/or
water-sensitive compounds were performed using the standard
Schlenk techniques. Organometallic compounds were handled
in a nitrogen-filled Vacuum Atmospheres drybox. High-resolu-
tion mass spectra were recorded on Micromass LCT or Micro-
mass Autospec. Elemental analyses were performed by At-
1
lantic Microlab (Nocross, GA). H and 13C NMR spectra were
recorded on Bruker Avance-500 or -400 spectrometers. Chemi-
cal shifts are reported relative to the residual solvent.
Materials. Toluene, dichloromethane, and diethyl ether are
obtained from the purified solvent system.27 High-pressure
polymerizations were performed in a mechanically stirred 600
mL Parr autoclave. Ultrahigh pure grade ethylene gas was
purchase from Airgas and used without further purification.
A 7% Al (wt %) solution of modified methylaluminoxane
(MMAO) in toluene (d ) 0.88 g/mL) containing 12% isobutyl
groups was purchased from Akzo Nobel. Acenaphthenequino-
ne, 1-hexene, 2-bromometaxylene, allylmagnesium chloride,
p-toluedine, and chloromethyltrimethylsilane were purchased
from Aldrich Chemical Co. Trimethylsilylmethyl azide was
purchased from TCI America. (DME)NiBr2 was obtaind from
Strem, and the second-generation Grubbs catalyst was a
generous donation from Materia, Inc.
9: 1H NMR(TCE 90 °C) δ 8.00 (d, J ) 8.2 Hz, 2H); 7.59 (s, br,
2H); 7.25 (br, 1H); 7.01 (d, J ) 7.4 Hz, 4H); 7.00 (t, J ) 7.3,
2H); 5.99 (s, 1H); 5.53 (s, 4H); 2.46 (br, 12H); 1.93 (br, 4H);
HRMS calcd for C36H32N2 [M + H]+ 493.2644, found 493.2647.
Synthesis of 3. Hydrogenation of the cyclophane 9 using
Pd on carbon in DCM/MeOH (1:1) was done under hydrogen
atmosphere for 3 h. The mixture was filtered thru Celite
(DCM/MeOH eluent) and after evaporation was subjected to
column chromatography (silica, DCM/hexane, 4:6) to give 3
in 92% yield.
3: 1H NMR(CD Cl ) δ 8.04 (d, J ) 8.4 Hz, 2H); 7.59 (s, br,
2
Synthesis of 6. A solution of 1-bromo-2,6-bis(bromomethyl)-
benzene 5 (13.2 g, 38.5 mmol) in THF/Et2O (1:1 mixture; 100
mL) was cooled to -78 °C and stirred for 20 min. A solution
of allylmagnesium chloride in THF (2 M, 2.5 equiv) was added
dropwise at -78 °C. The resulting solution was stirred
overnight and was allowed to warm to room temperature
naturally. The reaction was quenched with aqueous am-
monium chloride, then extracted with ether, washed with
brine, and dried over magnesium sulfate. The crude mixture
was chromatographed using silica and hexane as eluent to give
a colorless liquid in 90% yield.
2H); 7.11 (d, J )27.4 Hz, 4H); 7.02 (t, J ) 7.6, 2H); 2.32 (br,
8H); 1.84 (br, 4H); 1.46 (br, 4H); 1.27 (br, 8H); 13C NMR(CDCl )
3
148.1, 131.1, 128.6, 128.3, 127.2, 34.3, 31.6, 22.7 ppm; HRMS
calcd for C36H36N2 [M + H]+ 497.2957, found 497.2935.
Synthesis of PdCl2 Cyclophane Complex 10. A mixture
of (PhCN)2PdCl2 (18 mg, 0.07 mmol) and the macrocyclic ligand
3 (34.5 mg, 0.07 mmol) in CH2Cl2 (4 mL) was stirred at room
temperature overnight. After evaporation of all volatile com-
ponents, the residue was washed with pentane and dried.
High-quality single crystals of the complex were prepared by
layering decane on a concentrated CH2Cl2 solution of the
complex. The structure of the complex 10 was confirmed by
X-ray single-crystal structure analysis. 10: 1H NMR (500 MHz,
CDCl3) δ 8.18 (d, 2H, J ) 8.2 Hz), 7.55 (t, 2H, J ) 7.4 Hz),
7.32 (t, 2H, 6.8 Hz), 7.24-7.26 (m, 4H), 6.66 (d, 2H, J ) 7.3
Hz), 3.41 (br, 4H), 2.79 (br, 4H), 2.51-2.55 (m, 4H), 1.98-
2.03 (m, 4H), 1.54 (br, 4H), 1.26-1.33 (br, 4H); 13C NMR (125
MHz, CDCl3 in ppm) δ 147.1, 144.0, 134.2, 133.1, 131.0, 130.1,
129.2, 129.1, 125.7, 125.6, 34.4, 28.5, 25.8 ppm.
6: 1H NMR(CDCl ) δ 7.15 (m, 1H); 7.05 (m, 2H); 5.93-5.84
3
(m, 2H); 5.09-4.98 (m, 4H); 2.88-2.83 (m, 4H); 2.41-2.34 (m,
4H); 13C NMR(CDCl ) 141.6, 137.8, 127.9, 126.7, 114.9, 36.4, 33.8
ppm. Anal. Calcd3 for C14H17Br: C 63.41, H 6.46. Found: C
63.05, H 6.49.
Synthesis of 7. A solution of 6 (2.65 g, 10 mmol) in ether
was added dropwise to a flask filled with magnesium metals
(0.3 g, 1.2 equiv) and ether (40 mL). The formation of the
Grignard reagent is signaled by the refluxing action of ether.
If this does not occur, adding drops of dibromoethane activates
Synthesis of Pd(Me)Cl Cyclophane Complex 11. A
solution of (PhCN)2PdCl2 (416 mg, 1.08 mmol) in CH2Cl2 (18
mL) was cooled to -35 °C. Then tetramethyltin (0.52 mL, 3.80
mmol) was added, and the mixture was stirred at -35 °C for
two more hours. The ligand 3 (593 mg, 0.832 mmol) dissolved
(27) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.

Ni(II) and Pd(II) Complexes with Macrocyclic Ligand
Organometallics, Vol. 24, No. 21, 2005 4939
in 10.0 mL of CH2Cl2 was added to the in situ generated Pd-
(Me)Cl from the above solution. The resulting red solution was
warmed to RT and allowed to stir overnight. The solution was
filtered through Celite and subjected to flash chromatography
(DCM) under N2 flow, providing 11 as a dark red solid (722
mg, 81%).
followed by purging with 50 psi ethylene three times (5 min
each) at RT. After the catalyst solution was introduced at RT,
the reactor was immediately charged with ethylene to the
desired pressure (1 atm to 400 psi). The polymerization was
allowed to run for overnight. The desired temperature was
reached within 5 min after the catalyst was loaded into the
reactor. The reaction was stopped by the release of ethylene,
and removal of solvent afforded PEs.
1
11: H NMR (500 MHz, CDCl3) δ 8.17 (d, 1H, J ) 8.3 Hz),
8.13 (d, 1H, J ) 8.3 Hz), 7.51-7.61 (m, 2H), 7.21-7.32 (m,
6H), 6.88 (d, 1H, J ) 7.2 Hz), 6.65 (d, 1H, J ) 7.3 Hz), 3.28-
3.35 (m, 2H), 3.09-3.16 (m, 2H), 2.61-2.89 (m, 4H), 2.51-
2.60 (m, 4H), 1.80-1.93 (m, 4H), 1.48-1.55 (m, 2H), 1.33-
1.44 (m, 2H), 1.19-1.27 (m, 4H), 0.94 (s, 3H, Pd-Me); 13C NMR
(125 MHz, CDCl3 in ppm) δ 169.29, 164.78, 144.55, 144.26,
143.86, 132.81, 132.19, 131.42, 130.96, 129.74, 129.43, 129.38,
129.02, 127.59, 127.02, 126.79, 124.07, 123.98, 33.87, 28.15,
25.86, 25.36, 24.42, 5.05 ppm; HRMS calcd for C37H39N2ClPd
in CH3CN [M - Cl + CH3CN]+ 658.2428, found 658.2424.
Synthesis of Allyl Ni Cyclophane Complex 14. A
solution of ligand 3 (94 mg, 0.19 mmol), nickel allyl chloride
dimer (31 mg, 0.6 equiv), and sodium tetrakis[3,5-bis(trifluo-
romethyl)phenyl]borate (NaBAF) (170 mg, 0.19 mmol) in
diethyl ether (7 mL) was stirred at RT for 12 h. The resulting
reaction mixture was filtered through Celite, and the solvent
was evaporated in vacuo. The residue was washed with 10 mL
of pentane and dried, affording 180 mg (67% yield) of reddish
brown solid. High-quality single crystals were obtained by
recrystallization in toluene. The structure of complex 14 was
confirmed by X-ray single-crystal structure analysis.
Ethylene Polymerization by Ni-Allyl Complex 14.13,28
A 600 mL Parr autoclave was heated under vacuum at 135
°C for several hours and was flushed with ethylene twice. It
was then cooled to RT and backfilled with ethylene twice before
reducing the pressure inside. A solution of 14 (7.3 mg, 5 µmol)
in toluene (100 mL), which was prepared inside the glovebox,
was transferred into the Parr reactor under nitrogen stream.
The autoclave was sealed and the ethylene pressure raised to
200 psi. The solution was vigorously stirred under ethylene
pressure, and the temperature of the system was equilibrated
to be 5 degrees less than the desired polymerization temper-
ature for 15 min. The autoclave was then vented, and the
pressure inside was reduced. The activator, B(C6H5)3 (20 equiv,
51 mg, 100 µmol), dissolved in toluene (100 mL), was trans-
ferred into the autoclave, which was subsequently sealed and
pressurized to 200-400 psi ethylene pressure under vigorous
stirring. Polymerization was run at temperatures from 70 to
90 °C overnight. The reaction was stopped by the release of
ethylene, and removal of solvent afforded PEs.
1
14: H NMR (500 MHz, CDCl3) δ 8.22 (d, 2H, J ) 8.2 Hz),
Supporting Information Available: Detailed informa-
tion on X-ray crystal structural analyses for complexes 10 and
14. This material is available free of charge via the Internet
at http://pubs.acs.org.
7.72 (s, BAF- H), 7.61 (t, 2H), 7.56 (s, BAF- H), 7.32 (m, 6 H),
6.92 (d, 2H, J ) 7.2 Hz), 5.32 (m, 1H), 3.65 (s, b, 2H), 2.96-
2.45 (m, 12H), 1.88-1.26 (m, 14H); HRMS calcd for C71H53-
BF24N2Ni [M - BAF]+ 595.2623, found 595.2603.
Ethylene Polymerization by Preactivated PdII Com-
plexes 12. In a nitrogen-purged glovebox, 10 µmol of catalyst
was dissolved in 10 mL of toluene. Into a 600 mL Parr reactor
purged under nitrogen, 55 mL of toluene solvent was loaded
OM0503904
(28) Ionkin, A. S.; Marshall, W. J. Organometallics 2004, 23, 3276-
3283.